Alison M. Ferris

A novel optically accessible catalysis flow channel is introduced that enables quantitative, contiguous, two-dimensional in situ measurements of gas-phase temperature and species concentrations during heterogeneous catalytic reactions. Spatially resolved gas-phase Raman spectroscopy, integral Fourier-transform infrared spectroscopy, and catalyst-resolved infrared thermography establish a well-defined platform for studying coupled reaction–transport phenomena. Applied to the oxidative dehydrogenation of ethanol over iron–molybdenum oxide catalysts, spontaneous Raman measurements yielded two-dimensional profiles of nine gas-phase species—with limits of detection in the tens-to-hundreds-of-ppm range—and gas-phase temperature within 500 µm of the catalyst surface. Transport analysis in the boundary layer yielded a Lewis number of approximately 1.65, indicating dominant thermal diffusion near the surface, while axial Péclet numbers revealed diffusion-controlled heat transport but advection-dominated product transport in a laminar regime. Varying the bulk flow velocity did not significantly alter conversion or product distributions, indicating kinetic and diffusive control under the present conditions. An iron-rich catalyst formulation exhibited higher activity than stoichiometric , whereas temperatures above 511 K reduced selectivity due to increased formation of total-oxidation products. Catalyst-free experiments, supported by kinetic simulations, confirmed partial gas-phase oxidation of acetaldehyde to CO, CO 2 , acetic acid, methanol, formaldehyde, and peracetic acid. These results highlight the importance of local gas-phase contributions and demonstrate that spatially resolving the gas-phase thermochemistry enables the gas phase to act as a reporter of surface reactions and facilitates the decoupling of chemical processes from transport phenomena.

A novel optically accessible catalysis flow channel (CFC) is introduced that enables quantitative, contiguous, two-dimensional in situ measurements of gas-phase temperature and species con- centrations during heterogeneous catalytic reactions. Spatially resolved gas-phase Raman spec- troscopy, integral Fourier-transform infrared spectroscopy (FTIR) spectroscopy, and catalyst- resolved infrared (IR) thermography establish a well-defined platform for studying coupled reaction–transport phenomena. Applied to the oxidative dehydrogenation (ODH) of ethanol (EtOH) over iron–molybdenum (Fe–Mo) oxide catalysts, spontaneous Raman measurements yielded two-dimensional profiles of nine gas-phase species—with limits of detection (LODs) in the tens-to-hundreds-of-ppm range—and gas-phase temperature within 500 μm of the catalyst surface. Transport analysis in the boundary layer yielded a Lewis number of approximately 1.65, indicating dominant thermal diffusion near the surface, while axial Péclet numbers revealed diffusion-controlled heat transport but advection-dominated product transport in a laminar regime. Varying the bulk flow velocity did not significantly alter conversion or product distributions, indicating kinetic and diffusive control under the present conditions. An iron- rich catalyst formulation exhibited higher activity than stoichiometric Fe2(MoO4)3, whereas temperatures above 511 K reduced selectivity due to increased formation of total-oxidation prod- ucts. Catalyst-free experiments, supported by kinetic simulations, confirmed partial gas-phase oxidation of acetaldehyde (AcH) to CO, CO2, acetic acid (AcOH), methanol, formaldehyde, and peracetic acid. These results highlight the importance of local gas-phase contributions and demonstrate that spatially resolving the gas-phase thermochemistry enables the gas phase to act as a reporter of surface reactions and facilitates the decoupling of chemical processes from transport phenomena.

Laminar flame speed, temperature, and pressure measurements were conducted in high-temperature, spherically expanding ethane-air flames. The experiments were conducted in a shock tube, which allows access to a high-temperature regime previously under-explored for premixed ethane-air flames. The stoichiometric ethane-air mixtures were initially shock-heated to unburned gas conditions of 461-537 K, 1 atm. An Nd:YAG laser was used to spark-ignite the heated gas mixtures and initiate laminar flame propagation. High-speed, OH* endwall imaging was used to record the propagation of the spherically expanding flames in time, and the images were analyzed to determine the unburned, unstretched laminar flame speed. The measurements show close agreement with available literature results and kinetic model simulations (AramcoMech 3.0, NUIGMech1.3, and FFCM-2). A comprehensive survey of available ethane-air flame speed data was conducted to enable a high-fidelity power-law fit to describe the temperature dependence of ethane-air flame speeds. A single line-of-sight laser absorption diagnostic was additionally used to measure burned-gas temperature and pressure. The temperature and pressure measurements confirmed that flames generated using the shock-tube laminar flame method are adiabatic and constant-pressure. • Ethane-air laminar flame speed measurements were conducted at elevated temperatures (up to 537 K). • A new power-law fit describing the temperature dependence of stoichiometric ethane-air flame speeds (taking into account 79 data points generated in 17 different studies) is presented. • The first experimental study of temperature and pressure time-histories in the burned-gas region of laminar flames generated in a shock tube is presented.

High Resolution Image Download MS PowerPoint Slide In this study, we present a novel approach for time-resolved, in situ analysis of isotope scrambling reactions over platinum nanoparticle catalysts using high-sensitivity gas-phase Raman spectroscopy. A recently developed spectrometer setup enables detection limits in the hundreds of ppm, a dynamic range spanning four orders of magnitude in mole fraction, and a temporal resolution of one second. Experiments were performed by introducing D 2 gas to an H 2 -activated Pt nanoparticle catalyst in a closed sample, resulting in the formation of gaseous HD and H 2 . The time-resolved gas-phase mole fraction profiles show HD as the dominant product and only minor formation of H 2 . This observation is consistent with a predominantly associative exchange mechanism, in which D 2 reacts directly with surface-bound hydrogen to produce HD. A superimposed exchange involving trace water vapor was also observed, with stepwise conversion of H 2 O to HDO and D 2 O via surface-mediated reactions. Mole fractions were quantified using a spectral fitting routine based on simulated Raman spectra derived from literature polarizabilities and energy levels. The reaction quotient of the hydrogen isotopologues converged over time toward literature values of the equilibrium constant, and measurements at defined H 2 /D 2 ratios confirmed relative accuracies better than 2%. This Raman-based quantification method enables simultaneous, in situ detection of all relevant species with high accuracy and is ideally suited for studying transient, catalytic processes.

In this study, a new design for a 1D gas-phase Raman spectrometer is presented, utilizing two dedicated tracks to image different properties of the measured signal onto a single charge-coupled device (CCD) chip. Two possible configurations are shown: a polarization-separation configuration, which separates the detected Raman signal into s- and p-polarized shares; and a dual-resolution configuration, which captures all process-relevant species in a range of approximately 515-4650 cm −1 on one track and the highly resolved nitrogen spectrum on the other. This new spectrometer design offers several advantages when compared to traditional polarization-separation/dual-resolution systems, which often use switchable filters or two different spectrometers in tandem to achieve comparable measurements. Employing only one camera eliminates signal drift and minimizes calibration as well as spatial/spectral mapping issues. To validate instrument performance, the detection was paired with a continuous wave (CW) excitation system and used to measure in two generic but diagnostically challenging flow scenarios: flow near a heated surface, where thermal radiation is significant addressed by the polarization-separation configuration of the spectrometer and a channel flow at moderate temperatures in confined space, where the dual-resolution configuration of the spectrometer was employed. The results for both configurations and experiments showcase the instrument’s ability to effectively suppress background radiation (polarization-separation) or measure local gas-phase temperatures with higher accuracy (dual-resolution) and are complemented with resolution measurements yielding a maximum spatial resolution of 21.9 lp/mm along the 1D probe volume.